The subject matter relates to heat exchanger for a high flow rate infusion unit that pressurizes and warm fluids for infusion into a body at pressures equal to or exceeding gravity.
Infusion relates to the introduction of a fluid into a body, usually, although not necessarily, into vasculature. A fluid that is infused into a body may be termed an “infusate”. Such fluids may include, for example, blood, blood products, and solutions such as saline, antibiotics, and medications.
The combination of low operating room temperatures and the administration of anesthetics which inhibit a patient's thermoregulatory function leads to hypothermia during surgery. As is known, perioperative hypothermia can produce adverse outcomes such as surgical wound infection, extended hospitalization, and blood loss. See Sessler D I: Complications and Treatment of Mild Hypothermia. ANESTHESEOLOGY 2001; 95:531-543. Prevention or mitigation of hypothermia, particularly perioperative hypothermia, is thus a key clinical factor for successful treatment outcomes.
Hypothermia may be accelerated by infusion of fluid, especially if the fluid is refrigerated. For example, Sessler indicates that a unit of refrigerated blood or a liter of crystalloid solution at room temperature decreases the mean body temperature of adults by approximately 0.25° C. But patients suffering from serious trauma may require rapid infusion of large amounts of fluid, which can cause a sharp and sudden loss of heat in the body core, leading to a drop in mean core body temperature. In order to prevent or mitigate infusion-caused heat loss in a trauma patient, the infusate is often heated as it is administered.
Warming fluid prior to infusion into a human or animal body is known. See, for example the intravenous fluid warming systems and appliances described in the cross-referenced patent documents. See also the Ranger® blood/fluid warming system and products described at www.arizant.com, the web site of Arizant Healthcare Inc. The Ranger® blood/fluid warming system includes a heating appliance and a heat exchanger capable of being inserted into the heating appliance. Fluid flowing though the heat exchanger is warmed by contact between the heating appliance and heat exchanger, and then delivered intravenously to a patient. However, the disclosed systems cannot meet all rates of infusate delivery needed for treatment of trauma patients.
The technical challenges in heating a high volume of infusate delivered at a relatively high rate, for example, at 30 liters per hour (30 L/hr), or higher, include uniform transfer of heat to the fast-flowing fluid, elimination of air from the fluid, and an infusion system construction that supports convenience and speed of operation.
Solutions to these challenges in the prior state of the art include a known high speed infusion system that warms infusate by immersion of a heat exchanger in a warm water bath. A column of infusate flows through the heat exchanger, and the warm water bath heats the infusate as it passes through the heat exchanger. The heat, the flow pattern and high flow rate of the infusate create bubbles in the infusate, which must be removed before intravenous delivery in order to avoid formation of an air embolism in the patient being infused. This high speed infusion system includes a gas elimination device to collect bubbles from the infusate, and a clamp to halt the flow of infusate if air is detected in the infusate.
The known high speed infusion system is constituted of an appliance with a water heating and circulation system. The heat exchanger consists of a pair of coaxial tubes, a smaller one disposed inside a larger one. The infusate flows through the annulus between the larger and smaller tube, and the heated water is circulated from the heater, through the inner tube, and back to the heater. The heat exchanger is installed in the appliance where it must be reliably coupled to an infusate flow path and to a separate hot water flow path. The gas elimination device is separate from the heat exchanger; and it is installed separately and downstream from the heat exchanger. Infusate passes through the gas elimination device into a patient line for intravenous delivery to a patient. When a predetermined amount of air is detected in the gas elimination device, a downstream clamp is activated to pinch off the patient line, thereby stopping the flow of infusate to the patient. The heat exchanger and gas elimination device are discarded after each use, and new ones must be installed each time a patient is treated.
In this known high speed infusion system, the heat transfer mechanism poses a risk of an exchange of contaminants between the infusate and the water used to deliver heat. This may occur when the barrier between the water and the infusate is breached for some reason. The use of a warm water bath as the heat transfer mechanism requires continuous maintenance to keep the water clean and the pumping system operating with sufficient capacity. Air transported from infusate bags and bubbles generated from the infusate are collected and separated by the gas elimination device, and air is eliminated through a port in the device. At times, a large mass of collected bubbles can block the port, thereby preventing air from being vented. Then, the collected bubbles will cause detection of air that is not quickly vented, and the clamp will be activated. In such a case, the system can be restarted only after clearing or replacing the gas elimination device. In this known system, set up preceding each use requires separate handling and installation of the heat exchanger, the gas elimination device, and the length of patient line that is led through the clamp.
There is a need for a heat exchanger for high flow rate infusion that effectively transfers heat to a rapidly-flowing infusate without risk of contaminant exchange between the infusate and a heat transfer fluid. Another desirable advance would reliably eliminate air from the infusate without blocking an air vent. System set up would be improved by reduction of the number of devices required to be installed each time the system is used.